|the deep sea (2000 meters or more) where there is no light|
portion of the ocean deeper than about 2,000 m (6,600 feet) and shallower than about 6,000 m (20,000 feet). The zone is defined mainly by its extremely uniform environmental conditions, as reflected in the distinct life forms inhabiting it. The upper boundary between the abyssal zone and the overlying bathyal zone is conveniently defined as the depth at which the water temperature is 4 C (39 F); this depth varies between 1,000 and 3,000 m. Waters deeper than 6,000 m are treated separately as the hadal realm by ecologists.
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